In spite of silicon being the second most abundant element in nature bound as silicates in rocks and found solubilised as monomeric silicic acid in fresh and sea water it has not always been regarded as an essential nutrient in animal species.
Work conducted in the late 70's involving the removal of silicon from the diet of chickens and rats1,2 showed its role in the formation of bone density and connective tissues and follow up studies showed that collagen formation may be enhanced by the formation of proline and hydroxyproline in the presence of silicon3,4. Furthermore silicon has been found to be reduced in the serum of post menopausal women a group in which loss of bone density is common5. Silicon is thought to be essential in the diet but the precise mechanism by which it acts is uncertain and to date no metabolic processes involving silicon in animal species have been identified. However, it has been suggested that silicon aids the formation of glycosaminoglycan and collagen components of the bone matrix through its role as a constituent of the enzyme prolylhydrolase. Alternatively, silicon could have a structural role as a component of glycosaminoglycans and glycosamino-protein complexes, occurring as silanolate in mucopolysaccharides and linking different polysaccharides in the same polysaccharide chain, or linking acid mucopolysaccharides to protein. A number of recent studies have reinforced the suggestion that silicon is important in bone and connective tissue production. One involving a large study of over 2800 patients showed a significant link between the intake of silicon and bone mineral density6. A second study of cell lines in vitro showed orthosilicic acid to increase the formation of type 1 collagen, a component of connective tissue and bone7, and an improvement of sun damaged skin, hair and nail conditions when choline stabilised silicon was added to the diet in a double blind placebo study8.
Additionally silicon supplements have been shown to be beneficial in the training of horses where significant injury reduction has been achieved and in the raising of commercial animal stocks where silicon supplements (usually in the form of zeolites) are routinely administered. Recommendations on adequate nutritional intakes have not been established, either by COMA (Committee on Medical Aspects of Food and Nutrition Policy) or other advisory bodies however silicon deficiency has not been observed in humans. Dietary silicon intake is largely of plant origin including high levels particularly in grains such as oats, barley or rice, but this is essentially non bio-available due to the low solubility of silicon in water. Levels are lower in foods from animal sources. Silicon is also found in drinking water as orthosilicic acid which is its bioactive, assimilable form, and this is the source of most bio-available dietary silica with a 2 L consumption of water estimated to provide up to 10 mg of silicon in the form of monosilicic acid.
UK food supplements contain up to 500 mg silicon, but this is usually in the form of silica gels/sols, pulverised quartz or silica derived from plant material none of which are readily bioavailable.
Stabilised soluble silicon solutions have been described with quaternary ammonium compounds and these have been shown to provide high levels of bio-available silicon. However due to the nature of these complexes the liquid feed is supplied as a very caustic solution and potential for dosing errors and accidents in usage exist. Moreover, alternative sources of silica, such as potassium silicate are also caustic.
The inventors have shown that it is possible to recover the bioavailability from solids freeze dried from such stabilised caustic solutions and additionally recover the bioavailability of the same solids after mixing with organic acids (e.g. naturally occurring citric and tartaric acids) providing an internally compensated pH neutral product. Additionally the silicon source can be biogenic (from plant species such as rice or equisetum or possible diatomaceous origin). Silica from such species has a relatively high surface area and is found to dissolve rapidly in the stabilising medium. Typically, hydrolysed silicon tetrachloride which reacts violently with water, is irritating to eyes, respiratory system and skin, is used as the silicon source for quaternary ammonium stabilised silicon salts and hence the preferred use of biogenic silica is therefore an improvement on environmental and cost grounds.
A first aspect of the invention provides:
a food supplement comprising:    i) silica;    ii) a quaternary ammonium compound and/or a group Ia hydroxide    iii) an organic acid.
The inventors have found that combining the silica with at least one of a quaternary ammonium compound or group Ia hydroxide (e.g. sodium hydroxide or potassium hydroxide), together with the organic acid provides a source of bioavailable silica at a predictable dosage; allows the pH of the supplement if dissolved to be controlled, for example to a substantially neutral pH; and allows the dosage to be easily controlled by allowing the production of a solid product.
The inventors have also found that silicon salts, such as sodium silicate or potassium silicate (or sodium metasilicate or potassium metasilicate), may also be advantageously buffered with organic acids. This has the advantage of being able to be produced from readily available silicon salts, whilst still having enhanced bioavailablity and still being user friendly. Accordingly a further second aspect of the invention provides:
A food supplement comprising :    i) a Group Ia silicon salt; and    ii) an organic acid.
Preferably the Group Ia silicon salt is sodium silicate or potassium silicate. Typically the molar ratio of Na2SiO3:carboxylate groups on the organic acid is 1:2.
The nature of the product means that the final composition is preferably substantially non-toxic at the concentrations it is finally administered at which is intended to be around 200-1000 ppm as Si(OH)4.
Typically 60-80% of the silicon added to these solutions remains bio-active as determined by a modified colorimetric method described by R K Iler (R. K. Iler, The Chemistry of Silica, John Wiley & Sons, N.Y., 1979) which involves the formation of a complex between silicon and molybdenum and which is only sensitive to monosilicic acid or species which dissociate to monosilicic acid in the time frame of the experiment.
The quarternary ammonium salt and/or group Ia hydroxide, may be replaced by another basic salt which can prevent condensation of silanol groups by counter-ion stablisation of soluble anionic siloxy groups.
The term substantially neutral pH means a pH of between 6.0 and 8.0, more preferably between 6.5 and 7.5, more typically approximately pH 7.0.
Preferably, the silica solubilising agent is a tetraalkylammonium hydroxide, or sodium or potassium hydroxide.
Preferably the tetraalkylammonium hydroxide is tetraethyl, tetramethyl, tetrapropyl tetrabutyl or a combination thereof (to form a mixed alkylammonium hydroxide such as diethyldimethyl ammonium hydroxide, where alkyl is C1—C4) , but can be one of a number of naturally occurring quaternary ammonium compounds including carnitine, cholines and betaines.
The silica preferably has a surface area of at least 10 m2/g. However, having a larger surface area improves the solubility when mixed with the solubilising agent. The surface area may be at least 25, at least 50 or at least 100 m2/g
Potentially almost any source of silica or silicate can be used, including commercially produced silica from non-biological sources including fumed silica, silica gel and pulverised minerals. However, preferably the silica is biogenic silica derived from biological sources. This includes, for example diatomaceous earth, diatoms and silicified plant material
More preferably the biogenic silica is derived from multicellular plant material, such as from rice husks or Equisetum also known by the common name “horsetail”. Such biogenic silica is readily available from commercial sources.
Preferably the organic acid used according to any aspect of the invention is a C1—C6 (more preferably a C4, C5 or C6) carboxylic acid. It may be a straight chain or branched chain organic acid. It may comprise one or more hydroxyl groups however other chain lengths and levels of hydroxylation including the absence of hydroxyl groups can be used. The organic acid may be a naturally occurring organic acid such as ascorbic acid, citric acid or tartaric acid. The organic acid is typically an edible organic acid
Preferably wherein the molar ratio of silica to ammonium cation or group Ia cation is in the range of 1:1 up to 1:2, and may be 1:1.
The food supplement according to the invention may additionally comprise a liquid dispersant for example an oil, such as an edible oil. These include oils such as a vegetable oil, glycerol or paraffin. The term “vegetable oil” includes rape seed oil and olive oil. This may be admixed with the ingredients.
The paraffin is typically an edible, food grade of paraffin.
For example the silicate and organic acid may be mixed with oil prior to adding to the rest of the feed components, for example by wet mixing or spraying. Typically 5% w/w oil:feed mix is used.
The food supplement according to any preceding claim may be dried, in a substantially water free paste or in suspension. It may be pelleted for easier mixing with, for example a food stuff, it may also be dispersed in a water free liquid medium.
It may also be provided in drinking water.
The food supplement may also comprise one or more of the following: salt and/or carboxylate excipients, clay and/or talc or other bulking agents, sugars such as glucose, commercially available mineral premixes, soya meal, flavourings or liquid dispersant.
A further aspect of the invention also provides:
A method of producing a food supplement comprising:    a) mixing silica with a quaternary ammonium compound or a salt thereof in a solvent (for example water);    b) removing the solvent to form a solid; and    c) mixing an organic acid with the solid to form a food supplement.
Preferably sufficient organic acid is added to the solid so that when the mixture is dissolved in water, a substantially pH neutral solution is produced.
The invention also provides:
a method of producing a food supplement comprising mixing:    i) a Group Ia silicon salt; and    ii) an organic acid.
The food supplement preferably comprises one or more components as defined above for the first or second aspect of the invention.
The food supplement may be mixed with feed on manufacture of the feed. Alternatively it may be added substantially immediately prior to feeding to animals or humans or provided in the drinking water. In the latter case it may be added substantially immediately before providing the drinking water to the animal or human.
The invention also provides a food supplement obtainable by a method according to the invention.
Animal feed or human food comprising a food supplement according to the invention are also provided.
A method of providing dietary silica comprising providing a food supplement, animal feed, or human food according to the invention are still further provided.
The invention will now be described by way of example only.